Performs session validation for all open/active sessions in the system (those that have not been stopped or expired), and validates each one. If a session is found to be invalid (e.g. it has expired), it is updated and saved to the EIS.
This method is necessary in order to handle orphaned sessions and is expected to be run at a regular interval, such as once an hour, once a day or once a week, etc. The "best" frequency to run this method is entirely dependent upon the application and would be based on factors such as performance, average number of active users, hours of least activity, and other things.
Most enterprise applications use a request/response programming model. This is obvious in the case of web applications due to the HTTP protocol, but it is equally true of remote client applications making remote method invocations. The server essentially sits idle and only "works" when responding to client requests and/or method invocations. This type of model is particularly efficent since it means the security system only has to validate a session during those cases. Such "lazy" behavior enables the system to lie stateless and/or idle and only incur overhead for session validation when necessary.
However, if a client forgets to log-out, or in the event of a server failure, it is possible for sessions to be orphaned since no further requests would utilize that session. Because of these lower-probability cases, it might be required to regularly clean-up the sessions maintained by the system, especially if sessions are backed by a persistent data store.
Even in applications that aren't primarily based on a request/response model, such as those that use enterprise asynchronous messaging (where data is pushed to a client without first receiving a client request), it is almost always acceptable to utilize this lazy approach and run this method at defined interval.
Systems that want to proactively validate individual sessions may simply call the {@link #getSession(SessionKey) getSession(SessionKey)} method on any{@code ValidatingSessionManager} instance as that method is expected tovalidate the session before retrieving it. Note that even with proactive calls to {@code getSession}, this {@code validateSessions()} method should be invoked regularly anyway to
guarantee noorphans exist.
Note: Shiro supports automatic execution of this method at a regular interval by using {@link SessionValidationScheduler}s. The Shiro default SecurityManager implementations needing session validation will create and use one by default if one is not provided by the application configuration.